Treatment of anodized aluminum



United States Patent 3,216,866 TREATMENT OF ANODIZED ALUMINUM John Orlin, Cleveland Heights, Ohio, assignor to Allied Decals, Inc., Cleveland, ()hio, a corporation of Ohio No Drawing. Filed Mar. 6, 1961, Ser. No. 93,331 16 Claims. (Cl. his-6.1)

This invention relates to a new and useful method for decorating anodized aluminum surfaces and to new and useful compositions for use in this method.

Anodized aluminum surfaces have been decorated and colored by various methods. Most of these methods utilize the property of the anodized aluminum to readily receive dyes. One method of decoration consisted of pretreating the surface in the form of a design so that when dyed the color would not adhere 1n the areas so pretreated. This method proved somewhat unwieldy n that the artist or decorator could not properly ascertain the effects of his work until the article was finally subjected to the dye. The latter method also did not lend itself to the production of various shades of the same color.

Another method known in the art consisted of uniform dying of the anodized aluminum surface with subsequent treatment with nitric acid or the like so as to wholly or partially remove portions of the dye in a desired design. This method was accompanied by the undesirable feature of the artist being required to handle the strong corrosive and dangerous reagent such as nitric acid. Furthermore, the use of such a strong oxidizing agent as nitric acid made it very diflicult to achieve the partial removal of the dye necessary for shades and tones. If the solution is diluted to combat this undesirable defect the resulting solution is too weak to effect a complete dye removal when and if desired. In short, the latter method did not lend itself to the flexibility required for artistic decoration.

It is therefore an object of this invention to provide a simple method for artistically decorating anodized aluminum surfaces. A further object is to provide such a method which will effect various shades and tones of the same color on such articles as well as multicolored areas. A still further object is to provide such a method which can be effected by the use of relatively harmless and nontoxic reagents. Yet another object is to provide such reagents which will effect the desired results quickly and easily and without substantial alteration of the reagent composition during application. A further object is to provide such compositions which will react at a controlled rate so that the artist may vary the effects thereof during application by applying more or less material or by removal of excess material applied before it has time to react beyond the point at which a desired tone or shade would be produced.

Other objects and advantages of the present invention will become apparent as the following description proceeds.

To the accomplishment of the foregoing and related ends, the invention, then, comprises the features hereinafter fully described and particularly pointed out in the claims, the following description setting forth in detail certain illustrative embodiments of the invention, these being indicative, however, of but a few of the various Ways in which the principle of the invention may be employed.

An oxide coating may be formed on an aluminum surface by making the aluminum article the anode in an electrolytic cell using a solution of electrolyte such as sulfuric acid, chromic acid or oxalic acid. When the cell is connected to a source of electrical energy a coating of aluminum oxide is formed on the aluminum sur- 3,215,866 Patented Nov. 9, 1965 face. This coating is generally hard, adherent and adsorbent and is much thicker than the naturally occurring film of oxide present on all aluminum surfaces. The oxide coating may be produced by chemical means but will preferably be prepared by the anodic or electrolytic method. The term aluminous is intended to include aluminum articles as well as articles of aluminum base alloys.

The method of producing the oxide coating on the aluminous surface is not critical and it is only essential that the coating be suitably hard, adherent, and adsorbent to be effectively dyed. It is further desirable, but not essential, that the coating be not so thick as to receive an excessive amount of dye thus requiring excessive amounts of reagent for discoloring or alteration.

The anodized aluminous article is dyed, suitably by immersion in an aqueous solution of a dye. Preferably, a water-soluble direct or acid dye is used having a pH of from about 3.5 to 6. Particularly preferred are the sulfonic salts of -azo dyes having a pronounced acid character; Deep Black MLW has been found to be especially suitable. It is generally desirable to produce a uniformly colored surface or at least one with substantial areas of uniform color tone.

The decoration or alteration of the dyed surface is accomplished by the use of a reagent. The preferred reagents are aqueous solutions of compounds selected from the group consisting of alkali metal hydroxides and metal hypochlorites. Sodium hydroxide, potassium hydroxide, sodium hypochlorite and calcium hypochlorite are particularly preferred. Although the concentrations of these compounds in the solution are not critical, it is preferred to use concentrations from about 0.5 to about '2 percent by weight thereof to provide a sufficiently active reagent and at the same time a relatively harmless and nontoxic solution. The solution also contains an inhibitor effective to slow the reaction of the agent; a suitable inhibitor has been found to be sodium silicate. Although the concentration of the inhibitor is not critical, it is preferable to use it in the amount of from 0.05 to about 0.5 percent by weight of the reagent solution. Generally, the amount of inhibitor will be about 10 percent by weight of the reagent compound to be used. The addition of the inhibitor serves to slow the reaction of the reagent solution but does not materially limit the extent to which the reagent will act upon the dye. Thus, when a reagent solution containing an inhibitor is applied to the dyed surface the artist can see the extent to which color removal or alteration is taking place and remove excess solution, if necessary, to prevent errors. In the preferred embodiment of this invention, the reagent solution is used in a sufficiently dilute concentration so as to prevent its attacking the oxidized surface of the aluminous article. If this precaution is observed the oxide coated surface from which all dye has been removed will still be capable of receiving a new application of dye of either the same or of dilferent color to either correct errors or to permit the creation of multicolored effects on the article.

The above described reagent solution can be used in the form of a water solution of the reagent compound and the inhibitor. In this event, the solution is suitably applied by the artist by using a soft porous object such as sponge, cloth, a shaped cotton or absorbent paper wad, etc. These objects permit better control of the amount of liquid solution applied. These solutions may be varied somewhat by the addition of solvents and other ingredients to alter the effect of the solution on the dye. For example a solution containing 30 percent butyl carbitol, 10 percent diethylenetriamine, and 60 percent of a dilute sodium hydroxide-water solution has been found not only to effect some color removal on the dyed surface but also to produce a slightly different hue as well. Thus, reagent solutions containing different reagent compounds may produce different hues when applied to the same dye. Further, one given reagent solution may produce different hues when applied to dyes of the same color but of different chemical composition (e.g., dyes having different chromophore and auxochrome groups). It can therefore be seen that the selection of the reagent compound may be influenced by these factors.

It may be preferred to add the reagent solution in the form of pastes. These may be formed by adding silica gel or any other suitable gelling agent to the solution. The amounts of gelling agents may be varied widely depending upon the consistency of paste desired; the addition of approximately 5 percent silica gel to a sodium hydroxide-containing a reagent solution has been found quite suitable. When the reagent solution is in paste form the use of a brush applicator to effect the decoration has been found to be quite satisfactory,

The effect upon the dyed surface of the reagent solution used can be varied in different ways, for example, by the amount of solution applied or by the time of contact of the solution with the dyed surface. When small amounts of a liquid solution are applied in thin layers the evaporation of the water serves to terminate the decolorization reaction. When pastes are used excess quantities may be easily wiped from the surface or Washed off if desired. While the time required for decolorizing will vary with the amount and nature of the dye, and the amount, nature and concentration of the reagent solution, the time will generally be short enough so that the artist can readily see the result, and long enough so that he can also effect a removal of excess solution before excessive action takes place. As stated previously, the reagent solution can be used to entirely remove portions of the dye from the aluminous surface so as to permit redying and redecoration thereof. This process can be repeated as often as desired. Again, the redying may be done on a surface which was not entirely cleansed of the original dye to produce a mixing effect of the two dyes yielding a still different hue.

Once the desired image has been created on the dyed oxide coated aluminous surface, the surface may be sealed. The term image as used herein is meant to include any variation or deviation from a uniformly colored surface and therefore includes configurations, letters, designs, pictures or marks. The sealing step may be suitably conducted by immersion of the decorated, dyed, oxide coated aluminous surface in hot water. While the temperature and time of contact is not critical, it has been found that a period of immersion of from about 5 to about 30 minutes in an aqueous solution at a temperature of from about 180 to about 212 F., is preferred; a period of from to minutes in water just below the boiling point is particularly preferred. Actually, there is no upper limit to the period of immersion since once the sealing takes place, the article may be left in the aqueous solution indefinitely without further modification. The addition of accelerating additives such as nickel acetate and boric acid to hot water may be desirable. These additives are preferably added in such amounts as to produce a dilute aqueous solution having a pH of from about 5.0 to about 5.8. Once the sealing step is concluded the remaining dye on the surface of the aluminous article is sealed in and can no longer be removed by the use of the reagent solution. Further, the oxide coated surface of the article from which all dye had been removed by the reagent solution is no longer adsorbent after sealing and cannot be redyed. The sealed surface is of a high refractory nature having a hardness approaching 8 in the Mob scale.

One of the advantages of the instant invention is that it provides artists and decorators with a new safe and simple method of creating pictures and decorated articles.

Thus, kits can be sold for professional and educational purposes which contain sheets of dyed, anodized aluminum, various reagents and various dyes, together with suitable applicators. Artists using the method and compositions of this invention can produce artistic and decorative effects in a very short time with a high degree of aesthetic value. Using conventional brush and canvas, reproductions similar to these are only attainable through long diligent efforts by the most skillful artists. This invention may be practiced on any anodized aluminous article regardless of shape or form. The relative safety of the materials of this invention also enhances its use to the trade.

Other modes of applying the principle of the invention may be employed, change being made as regards the details described, provided the features stated in any of the following claims or the equivalent of such be employed.

I, therefore, particularly point out and distinctly claim as my invention:

l. A process for producing an image on an oxidecoated aluminous surface which comprises impregnating said surface with a water-soluble organic dye having a pH from about 3.5 to 6 and applying to selected areas of said surface an aqueous solution containing from about 0.5 to about 2 percent by weight of a reagent compound selected from the group consisting of alkali metal hydroxides and metal hypochlorites, said solution containing from about 0.05 to about 0.5 percent by weight of sodium silicate, and sealing said image produced by immersing said surface in hot water.

2. A process according to claim 1, wherein said reagent compound is sodium hydroxide.

3. A process according to claim 1, wherein said reagent compound is potassium hydroxide.

4. A process according to claim ll, wherein agent compound is sodium hypochlorite.

5. A process according to claim 1, wherein said reagent compound is calcium hypochlorite.

6. A process according to claim ll, wherein said sealing step comprises immersing in water at a temperature from about to 212 F. for about 10 to 20 minutes.

'7. A process according to claim 1, wherein said hot water contains, in dilute solution, an acidic additive selected from the group consisting of nickel acetate and boric acid.

8. A process according to claim 1, wherein said aqueous solution containing reagent compound is in the form of a paste.

9. A composition for decolorizing the dyed, oxidecoated surface of an aluminous article which comprises an aqueous solution containing from about 0.5 to about 2 percent by weight of a decolorizing reagent compound capable of decolorizing dyed oxide-coated aluminous surfaces selected from the group consisting of alkali metal hydroxides and metal hypochlorites, said solution containing from about 0.05 percent to about 0.5 percent by weight of sodium silicate to inhibit effectively the normal action of such decolorizing reagent.

10. A composition according to claim 9, reagent compound is sodium hydroxide.

11. A composition according to claim 9, reagent compound is potassium hydroxide.

12. A composition according to claim 9, reagent compound is sodium hypochlorite.

13. A composition according to claim 9, reagent compound is calcium hypochlorite.

14. A composition according to claim 9, wherein said aqueous solution contains a gelling agent in sufficient quantity to form a paste of said composition.

15. A composition according to claim 14. wherein said gelling agent is silica gel.

16. A composition for decolorizing the dyed, oxidecoated surface of an aluminous article which comprises said rewherein said wherein said wherein said wherein said 5 6 about 30 percent butyl carbitol, about 10 percent diethyl- 2,431,728 12/47 Bergstein 1486.14 enetriamine and about 60 percent of a dilute aqueous 2,460,898 2/49 Meyer 1486.14 sodium hydroxide solution, said solution containing a 2,811,456 10/57 Coleman 1486.15 small amount of sodium silicate suflicient substantially 2,927,872 3/60 Cohn 1486.1 to slow the action of said composition. 5 ,293 6/61 Cybriwsky et al. 1486.1 X

References Cited by the Examiner FOREIGN PATENTS 876,462 4/42 France.

UNITED STATES PATENTS M k 252 1 7 X OTHER REFERENCES Forbes 252-187 X 10 Light Metals, October 1949, pp. 536-542. Phair et al. 252-187 X Johnson X RICHARD D. NEVIUS, Primary Exammer. Pettit.

MARCUS U. LYONS, Examiner. 

1. A PROCESS FOR PRODUCING AN IMAGE ON AN OXIDECOATED ALUMINOUS SURFACE WHICH COMPRISES IMPREGNATING SAID SURFACE WITH A WATER-SOLUBLE ORGANIC DYE HAVING A PH FROM ABOUT 3.5 TO 6 AND APPLYING TO SELECTED AREAS OF SAID SURFACE AN AQUEOUS SOLUTION CONTAINING FROM ABOUT 0.5 TO ABOUT 2 PERCENT BY WEIGHT OF A REAGENT COMPOUND SELECTED FROM THE GROUP CONSISTING OF ALKALI METAL HYDROXIDES AND METAL HYPOCHLORITES, SAID SOLUTION CONTAINING FROM ABOUT 0.05 AT ABOUT 0.5 PERCENT BY WEIGHT OF SODIUM SILICATE, AND SEALING SAID IMAGE PRODUCED BY IMMERSING SAID SURFACE IN HOT WATER. 